This invention relates to a diffusion barrier layer and method comprising same upon which a metal film, preferably a copper film, is deposited thereupon. More specifically, the present invention relates to a diffusion barrier layer and method comprising same that improves the adhesion between the diffusion barrier layer and the metal layer.
As the microelectronics industry evolves into ultra-large-scale integration (ULSI), the intrinsic properties of typical metallization materials become the limiting factor in advanced circuit design and manufacture. Aluminum, which has been widely used as the interconnect metal, suffers from several drawbacks such as relatively high electrical resistivity and susceptibility to electromigration which may curtail its usefulness. Other metallization materials, such as tungsten and molybdenum, provide a high migration resistance but also have a high electrical resistance that prevents an integrated circuit incorporating these materials from being operated at high speed. Because of its low resistivity and enhanced resistance to electromigration, copper is an attractive material for high-speed integrated circuits. Still other candidates being considered for use as a metallization material include platinum, cobalt, nickel, palladium, ruthenium, rhodium, iridium, gold, silver and alloys comprising same.
Numerous methods such as ionized metal plasma (IMP), physical vapor deposition (PVD), chemical vapor deposition (CVD), atomic layer deposition (ALD), plasma-assisted chemical vapor deposition (PACVD), plasma-enhanced chemical vapor deposition (PECVD), electroplating, and electroless plating have been used to deposit a metal film such as copper upon a barrier layer. Among them, CVD and ALD methods using one or more organometallic precursors may be the most promising methods because these methods provide excellent step coverage for high aspect ratio structures and good via filling characteristics.
Several organometallic precursors have been developed to deposit low electrical resistivity copper films by the aforementioned processes, particularly CVD or ALD processes. Two of the most useful families of copper CVD precursors that have been studied extensively are the Cu (I) and Cu (II) β-diketonates. The Cu (II) precursors require use of an external reducing agent such as hydrogen or alcohol to deposit copper films that are largely free of impurities, while Cu (I) precursors can deposit pure copper films without using an external reducing agent via a bimolecular disproportionation reaction that produces a Cu (II) β-diketonate as a volatile byproduct. The β-diketonate ligand most often present in these precursors is hexafluoroacetylacetonate or the hfac anion [OC(CF3)CHC(CF3)O]. A particularly effective CVD copper precursor is 1,1,1,5,5,5-hexafluoro-2,4-pentanedionato-copper (I) trimethylvinylsilane (hereinafter Cu(hfac)(tmvs)), which is sold under the trademark CUPRASELECT™ by the Schumacher unit of Air Products and Chemicals, Inc., Carlsbad, Calif., the assignee of the present invention.
A barrier layer is typically utilized in conjunction with a metal or copper layer to prevent detrimental effects caused by the interaction or diffusion of the metal or copper layer with other portions of the integrated circuit. Exemplary barrier materials include metals, such as titanium, tantalum, tungsten, chromium, molybdenum, zirconium, vanadium, and carbides, nitrides, carbonitrides, silicon carbides, silicon nitrides, and silicon carbonitrides of these metals where they consitute a stable composition. In some instances, the initial deposition of CVD or ALD metal or copper film on the barrier layer may function as a seed layer, e.g., an adhesive, conducting seed layer to facilitate further deposition of a subsequent metal layer such as copper by electrochemical plating, electroless plating, or by PVD, CVD, or ALD methods to complete the thin-film interconnect.
Despite the foregoing developments, the integrated circuit (IC) industry is presently experiencing difficulty forming adherent metal or copper films on diffusion barrier layer materials. A variety of solutions to this problem have been proposed. For example, Gandikota et al., Microelectronic Engineering 50, 547-53 (2000), purports to improve adhesion between a CVD copper thin film and barrier layers by: (a) depositing a copper flash layer on the barrier layer by physical vapor deposition (PVD) prior to chemical vapor deposition, or (b) annealing the CVD copper layer after deposition. See also Voss et al., Microelectronics Engineering 50, 501-08 (2000). Unfortunately, these methods are not acceptable to the IC industry because they add to the equipment requirements for the copper deposition step. In addition, annealing, particularly at elevated temperatures, can have deleterious effects on the overall product.
U.S. Pat. No. 5,019,531 discloses a CVD process for depositing copper on a substrate selected from the group consisting of aluminum, silicon, titanium, tungsten, chromium, molybdenum, zirconium, tantalum, vanadium and silicides thereof using an organic complex or organometallic compound of copper. The organic complex or organometallic compound is selected from β-diketonate and cyclopentadienyl compounds of copper such as bis-acetylacetonato-copper, bis-hexafluoroacetylacetonato-copper, bis-dipivaloylmethanato-cooper, dimethyl-gold-hexafluoroacetylacetonato, cyclopentadienyl-triethylphosphine-copper, and dimethyl-gold-acetylacetonato. The adhesion of the copper on the substrate, however, was poor.
As mentioned previously, one method to form a copper film unto a substrate having a barrier layer deposited thereupon is through plasma enhanced or plasma assisted chemical vapor deposition. The reference, Eisenbraun et al., “Enhanced Growth of Device-Quality Copper by Hydrogen Plasma-Assisted Chemical Vapor Deposition” published in Appl. Phys. Letter, 1992), describes a PACVD process for depositing copper using β-diketonate precursors. According to Eisenbraun, the copper precursor is reduced by atomic and ionic hydrogen species to deposit copper on the substrate. The reference, Jin et al., Plasma-Enhanced Metal Organic Chemical Vapor Deposition of High Purity Copper Thin Films Using Plasma Reactor with the H Atom Source” published in J. Vac. Sci. Technology A, 1999, also discloses a plasma-enhanced technique to deposit pure copper using Cu(II) bis(hexafluoroacetylacetonato), Cu(II)(hfac), as an organometallic precursor. Likewise, the reference, Laksmanan et al., “A Novel Model of Hydrogen Plasma Assisted Chemical Vapor Deposition of Copper” and published in Thin Solid Films, 1999, describes a hydrogen-plasma assisted process for depositing copper on a barrier layer. Although, the aforementioned references were successful in depositing a metallic, continuous, dense device-quality copper film with conformal step coverage that was virtually free from heavy element contaminants, the adhesion of copper on the substrate was unacceptable.
U.S. Pat. Nos. 5,085,731, 5,094,701 and 5,098,516 (referred to collectively as Norman) describe a thermal CVD process for depositing a copper film with low electrical resistivity by using a volatile liquid organometallic copper precursor such as Cu(hfac)(tmvs) at relatively low temperatures onto metallic substrates. Further, the reference, Norman et al. “Chemical Additives for Improved Copper Chemical Vapor Deposition Processing”, Thin Solid Films, 1995, describes the use of tmvs and hfac ligands alone or in combination with water to improve deposition of copper. This deposition was achieved, however, with limited success. Numerous other researchers investigated the use of tmvs and hfac ligands alone or in combination with water to improve deposition of copper with limited or no success (e.g., Petersen et al. “Enhanced Chemical vapor Deposition of Copper from (hfac)Cu(TMVS) Using Liquid Coinjection of TMVS”, J. Electrochem. Soc., 1995; Gelatos et al. “Chemical Vapor Deposition of Copper from Cu+1 Precursors in the Presence of Water Vapor” Appl. Phys. Letter, 1993; Japanese Unexamined Patent Publication JP 2000-219968A; and U.S. Pat. No. 6,165,555).
Other organometallic copper precursors, such as (hfac)Cu(I)(MP) where MP is 4-methyl-1-pentene and (hfac)Cu(I)(DMB) where DMB is 3,3-dimethyl-1-butene, have been used to deposit low resistivity copper films on silicon wafers coated with titanium nitride (Kang et al., “Chemical Vapor Deposition of Copper Film”, Thin Solid Films, 1999). In the reference, Hwang et al., “Surfactant-Catalyzed Chemical Vapor Deposition of Copper Thin Films”, Chem. Mater., 2000, a submonolayer of iodine has been used to facilitate deposition of copper films from Cu(hfac)(tmvs) with a smooth surface and at a greatly enhanced rate. None of these techniques, however, discusses the quality of the CVD deposited copper film on the barrier layer.
U.S. Pat. No. 6,423,201 B1 describes the use of a thin silicon layer at the top of a TiN barrier layer to improve adhesion. It is, however, not desirable to deposit copper directly on silicon due to the formation of copper silicon alloys which exhibit high resistivity.
The adhesion of copper to the underlying barrier materials has also been reported to be problematic by several researchers. For example, the deposition of copper on titanium nitride substrate using Cu(I)(hfac)(tmvs) precursor (or CUPRASELECT™) has been reported to be poor (Nguyen, T. and Evans, D. R., “Stress and Adhesion of CVD Copper and TiN”, Mat. Res. Soc. Symp. Proc., 1995 and Nguyen, T. and Evans, D. R., “Stress and Adhesion of CVD Copper and TiN”, Mat. Res. Soc. Symp. Proceeding, 1995). It has been reported that the direct deposition of CVD copper on a diffusion barrier leads to the formation of a fluorine, carbon and oxygen containing amorphous layer between the copper film and barrier layer that is responsible for poor adhesion, as discussed by Kroger, R. et al. in papers “Nucleation and Growth of CVD Copper Films” published in Mat. Res. Soc. Symp. Proceeding, 1999 and “Properties of Copper Films Prepared by Chemical Vapor Deposition for Advanced Metallization of Microelectronic Devices” published in J. Electrochemical Society, 1999. The amorphous layer is believed to be formed during very early stages of CVD copper deposition from the by-products of the Cu (I) precursor. Similar adhesion problems on barrier layer have been reported with Cu (II) precursors.
The reference WO 00/71550 discusses limiting the formation of a fluorine, carbon and oxygen containing amorphous layer on the barrier layer by reducing and/or eliminating the amount of fluorine present in the copper precursors. However, these attempts have not yet resulted in the desired results.
Reduction of copper precursors like Cu (II) bis-(2,2,6,6-tetramethyl-3,5-heptanedionate) with hydrogen and Cu (II) bis-(1,1,1,5,5,5-hexafluoroacetylactonate) hydrate with methanol, ethanol, and formalin have been tried to deposit copper by atomic layer epitaxy on a variety of barrier layers with limited success, as described by Martensson and Carlsson in “Atomic Layer Epitaxy of Copper”, J. Electrochem. Soc., 2000 and Solanki and Pathangey in “Atomic Layer Deposition of Copper Seed Layers”, Electrochemical and Solid-State Letters, 2000.
The reference, Holloway et al. in a paper “Tantalum as a Diffusion Barrier Between Copper and Silicon: Failure Mechanism and Effect of Nitrogen Additions” published in J. Appl. Physics, 1992, relates that tantalum nitride (Ta2N) is an excellent barrier to copper penetration. However, the reference fails to discuss the deposition of copper by CVD on tantalum nitride nor the quality of CVD copper adhesion onto the tantalum nitride.
The barrier properties of CVD and sputtered tantalum nitride have been studied and compared by Tsai et al. in a paper “Comparison of the Diffusion Barrier Properties of Chemical-Vapor Deposited and Sputtered TaN between Cu and Si” published in J. Appl. Physics, 1996. However, the reference fails to discuss the deposition of copper by CVD on tantalum nitride nor the quality of CVD copper adhesion onto the tantalum nitride.
Despite the foregoing developments, there remains a need to develop a process to improve the adhesion of a metal, particularly a copper, film deposited on a diffusion barrier layer by CVD or ALD. Further, there is a need for a process to improve the adhesion of the metal film onto the barrier layer without incurring additional equipment requirements or an annealing step.
All references cited herein are incorporated herein by reference in their entireties.